Currently, in the CATV (hereinafter sometimes cable) industry, technicians perform a series of tests at multiple points in a subscriber location before an installation is deemed “Quality” or “Clean.” This process is known as certification. It creates what is known as a “birth certificate” for the subscriber premises. The management of a multi-system operator (hereinafter sometimes MSO) or smaller cable system operator identifies certain system performance limits that must be passed in order to certify the subscriber location as ready for connection to the system. As an example, the operator's home certification program might require the operator's installation and service technicians to run tests at different points in the distribution circuit at the subscriber's location (for example, home, apartment building, or place of business) in a certain order with certain limits on the test results at each point.
Another problem is with cable systems switching to digital. Leakage from analog cable channels is readily detected by systems, generally referred to as “taggers,” of the general types illustrated in, for example, U.S. Pat. Nos. 5,608,428; 6,018,358; 6,804,826, and references cited therein. The disclosures of these references are hereby incorporated herein by reference. This listing is not intended to be a representation that a complete search of all relevant art has been made, or that no more pertinent art than that listed exists, or that the listed art is material to patentability. Nor should any such representation be inferred.
However, distinct from an analog channel, a digital channel signal is spread fairly uniformly over 6 MHz. As a result, there is too little “tag” signal power in any sample, or “slice,” of the 6 MHz digital signal to reliably render the tag signal detectable.
A solution to this problem of tagging digital signals is to put a single frequency tag signal in the gap between adjacent 6 MHz digital channels and then monitor the gap in an effort to detect the tag. If the tag is detected, the operator has detected a leak. An enhancement puts multiple, for example, two, tag signals in the gap at multiple, for example, two, frequencies spaced far enough apart to discriminate between them. The operator looks for both/all of the inserted signals in order to detect a leak. The use of multiple tag signals at multiple different frequencies is useful where, for example, systems are overbuilt. Examples of these and similar techniques are described in, for example, PCT publication WO 2013/003301. Again, the disclosure of this reference is hereby incorporated herein by reference. This listing is not intended as a representation that a complete search of all relevant art has been made, or that no more pertinent art than that listed exists, or that the listed art is material to patentability. Nor should any such representation be inferred.